well,I'm not saying that as an individual, your score on Jan 30 would equal your score on the 31st. It could vary by even 10 points. While some people will certainly score better on one versus the other (based on their strengths/weaknesses in preparation), and based on curves, the average/deviations are not changing for either test. Some people might be prone to careless errors, but have a firm understanding of the material, and they may do better on the harder test with a lenient curve. But for every one person who is like this, there may be another who understands the basics really well, nails those questions down like clockwork, and therefore benefits from an easy test with a hard curve. So sure, an individual may benefit from one versus another based on strengths/weakenesses/standardized testing ability, but the collective whole is most certainly not at an advantage to having the 'hard' versus 'easy' one.
And also, it's really hard to make a generalization about which category one falls into before sitting in. Since we never will know what the curves are, what questions we are getting right/wrong, which one of those 'hard questions' are actually just experimental, the exact extent of 'hard' vs. 'easy' and the exact pros/cons of taking each exam, we can only speculate as to which type of test we may prefer. My point, I guess, is that someone should not pre-define themselves into a category before test day, and then the second they figure out that this is the 'hard' test, void it...